RESUMO
Deficiency in meiotic recombination leads to aberrant chromosome disjunction during meiosis, often resulting in the lethality of gametes or genetic disorders due to aneuploidy formation. Budding yeasts lacking Spo11, which is essential for initiation of meiotic recombination, produce many inviable spores in meiosis, while very rarely all sets of 16 chromosomes are coincidentally assorted into gametes to form viable spores. We induced meiosis in a spo11∆ diploid, in which homolog pairs can be distinguished by single nucleotide polymorphisms and determined whole-genome sequences of their exceptionally viable spores. We detected no homologous recombination in the viable spores of spo11∆ diploid. Point mutations were fewer in spo11∆ than in wild-type. We observed spo11∆ viable spores carrying a complete diploid set of homolog pairs or haploid spores with a complete haploid set of homologs but with aneuploidy in some chromosomes. In the latter, we found the chromosome-dependence in the aneuploid incidence, which was positively and negatively influenced by the chromosome length and the impact of dosage-sensitive genes, respectively. Selection of aneuploidy during meiosis II or mitosis after spore germination was also chromosome dependent. These results suggest a pathway by which specific chromosomes are more prone to cause aneuploidy, as observed in Down syndrome.
Assuntos
Aneuploidia , Meiose , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae , Humanos , Cromossomos/metabolismo , Endodesoxirribonucleases/genética , Recombinação Homóloga , Meiose/genética , Meiose/fisiologia , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismoRESUMO
Protein glycosylation regulates many cellular processes. Numerous glycosyltransferases with broad substrate specificities have been structurally characterized. A novel inverting glycosyltransferase, EarP, specifically transfers rhamnose from dTDP-ß-L-rhamnose to Arg32 of bacterial translation elongation factor P (EF-P) to activate its function. Here we report a crystallographic study of Neisseria meningitidis EarP. The EarP structure contains two tandem Rossmann-fold domains, which classifies EarP in glycosyltransferase superfamily B. In contrast to other structurally characterized protein glycosyltransferases, EarP binds the entire ß-sheet structure of EF-P domain I through numerous interactions that specifically recognize its conserved residues. Thus Arg32 is properly located at the active site, and causes structural change in a conserved dTDP-ß-L-rhamnose-binding loop of EarP. Rhamnosylation by EarP should occur via an SN2 reaction, with Asp20 as the general base. The Arg32 binding and accompanying structural change of EarP may induce a change in the rhamnose-ring conformation suitable for the reaction.
Assuntos
Arginina/química , Proteínas de Bactérias/metabolismo , Glicosiltransferases/metabolismo , Fatores de Alongamento de Peptídeos/metabolismo , Ramnose/química , Cristalografia por Raios X , Dissulfetos , Escherichia coli/metabolismo , Glicosilação , Cinética , Mutação , Neisseria meningitidis/metabolismo , Açúcares de Nucleosídeo Difosfato , Ligação Proteica , Domínios Proteicos , Estrutura Secundária de Proteína , Nucleotídeos de TiminaRESUMO
DNA polymerases are useful tools in various biochemical experiments. We have focused on the DNA polymerases involved in DNA replication including the unnatural base pair between 7-(2-thienyl)imidazo[4,5-b]pyridine (Ds) and 2-nitro-4-propynylpyrrole (Px). Many reports have described the different combinations between unnatural base pairs and DNA polymerases. As an example, for the replication of the Ds-Px pair, Deep Vent DNA polymerase exhibits high efficiency and fidelity, but Taq DNA polymerase shows much lower efficiency and fidelity. In the present study, we determined the crystal structure of Deep Vent DNA polymerase in the apo form at 2.5 Å resolution. Using this structure, we constructed structural models of Deep Vent DNA polymerase complexes with DNA containing an unnatural or natural base in the replication position. The models revealed that the unnatural Ds base in the template-strand DNA clashes with the side-chain oxygen of Thr664 in Taq DNA polymerase, but not in Deep Vent DNA polymerase.
Assuntos
DNA Polimerase Dirigida por DNA/química , Proteínas Arqueais/química , Pareamento de Bases , Sítios de Ligação , Cristalografia por Raios X , DNA/química , Modelos Moleculares , Pyrococcus/enzimologia , Homologia Estrutural de Proteína , Taq Polimerase/químicaRESUMO
The putative translation elongation factor Mbar_A0971 from the methanogenic archaeon Methanosarcina barkeri was proposed to be the pyrrolysine-specific paralogue of EF-Tu ("EF-Pyl"). In the present study, the crystal structures of its homologue from Methanosarcina mazei (MM1309) were determined in the GMPPNP-bound, GDP-bound, and apo forms, by the single-wavelength anomalous dispersion phasing method. The three MM1309 structures are quite similar (r.m.s.d. < 0.1 Å). The three domains, corresponding to domains 1, 2, and 3 of EF-Tu/SelB/aIF2γ, are packed against one another to form a closed architecture. The MM1309 structures resemble those of bacterial/archaeal SelB, bacterial EF-Tu in the GTP-bound form, and archaeal initiation factor aIF2γ, in this order. The GMPPNP and GDP molecules are visible in their co-crystal structures. Isothermal titration calorimetry measurements of MM1309·GTP·Mg(2+), MM1309·GDP·Mg(2+), and MM1309·GMPPNP·Mg(2+) provided dissociation constants of 0.43, 26.2, and 222.2 µM, respectively. Therefore, the affinities of MM1309 for GTP and GDP are similar to those of SelB rather than those of EF-Tu. Furthermore, the switch I and II regions of MM1309 are involved in domain-domain interactions, rather than nucleotide binding. The putative binding pocket for the aminoacyl moiety on MM1309 is too small to accommodate the pyrrolysyl moiety, based on a comparison of the present MM1309 structures with that of the EF-Tu·GMPPNP·aminoacyl-tRNA ternary complex. A hydrolysis protection assay revealed that MM1309 binds cysteinyl (Cys)-tRNA(Cys) and protects the aminoacyl bond from non-enzymatic hydrolysis. Therefore, we propose that MM1309 functions as either a guardian protein that protects the Cys moiety from oxidation or an alternative translation factor for Cys-tRNA(Cys).
Assuntos
Proteínas Arqueais/química , Guanosina Trifosfato/química , Methanosarcina/química , RNA de Transferência de Cisteína/química , Sequência de Aminoácidos , Proteínas Arqueais/genética , Proteínas Arqueais/metabolismo , Calorimetria , Cristalografia por Raios X , Guanosina Difosfato/química , Guanosina Difosfato/metabolismo , Guanosina Trifosfato/metabolismo , Guanilil Imidodifosfato/química , Guanilil Imidodifosfato/metabolismo , Cinética , Methanosarcina/genética , Methanosarcina/metabolismo , Modelos Moleculares , Dados de Sequência Molecular , Estrutura Molecular , Conformação de Ácido Nucleico , Fator Tu de Elongação de Peptídeos/química , Fator Tu de Elongação de Peptídeos/genética , Fator Tu de Elongação de Peptídeos/metabolismo , Fatores de Alongamento de Peptídeos/química , Fatores de Alongamento de Peptídeos/genética , Fatores de Alongamento de Peptídeos/metabolismo , Fatores de Iniciação de Peptídeos/química , Fatores de Iniciação de Peptídeos/genética , Fatores de Iniciação de Peptídeos/metabolismo , Ligação Proteica , Estrutura Terciária de Proteína , RNA de Transferência de Cisteína/metabolismo , Homologia de Sequência de AminoácidosRESUMO
One of the modified nucleosides that frequently occurs in rRNAs and tRNAs is 5-methylcytidine (m5C). Escherichia coli Fmu/RsmB/RrmB is an S-adenosyl-L-methionine (AdoMet)-dependent methyltransferase that forms m5C967 in 16S rRNA. Fmu/RsmB/RrmB homologues exist not only in bacteria but also in archaea and eukarya and constitute a large orthologous group in the RNA:m5C methyltransferase family. In the present study, the crystal structure of a homologue of E. coli Fmu/RsmB/RrmB from the archaeon Pyrococcus horikoshii (PH0851) complexed with an AdoMet analogue was determined at 2.55 Å resolution. The structure and sequence of the C-terminal catalytic domain are highly conserved compared with those of E. coli Fmu/RsmB/RrmB. In contrast, the sequence of the N-terminal domain is negligibly conserved between the bacterial and archaeal subfamilies. Nevertheless, the N-terminal domains of PH0851 and E. coli Fmu/RsmB/RrmB are both α-helical and adopt a similar topology. Next to the AdoMet-binding site, a positively charged cleft is formed between the N- and C-terminal domains. This cleft is conserved in the archaeal PH0851 homologues and seems to be suitable for binding the RNA substrate.
Assuntos
Metiltransferases/química , Pyrococcus horikoshii/enzimologia , Sequência de Aminoácidos , Escherichia coli/enzimologia , Proteínas de Escherichia coli/química , Modelos Moleculares , Dados de Sequência Molecular , Conformação de Ácido Nucleico , Estrutura Terciária de Proteína , RNA Ribossômico 16S/química , RNA Ribossômico 16S/metabolismo , Alinhamento de Sequência , Homologia Estrutural de ProteínaRESUMO
Methods for fluorescent probing at a defined position of RNA provide powerful tools for analyzing the local structural conformation of functional RNA molecules by tracking fluorescence changes. In this article, we describe the site-specific fluorescent probing of RNA by transcription with an expanded genetic alphabet, using an extra, unnatural base pair between 2-amino-6-(2-thienyl)purine (s) and pyrrole-2-carbaldehyde (Pa). The protocol comprises template DNA preparation containing Pa, transcription involving fluorescent s incorporation and structural analysis of transcripts. The s base is strongly fluorescent, and its nucleoside 5'-triphosphate is site-specifically incorporated into RNA transcripts, opposite Pa in DNA templates, by conventional T7 transcription. The fluorescent intensity of s changes depending on its environment around the probe site, providing clues about the local structural features of RNA molecules. This is the first protocol for RNA transcript preparation with fluorescent labeling at a desired position. The procedure for s-containing RNA preparation takes about 2-3 d.
Assuntos
Pareamento de Bases/genética , Corantes Fluorescentes/química , Purinas/química , RNA/química , RNA/ultraestrutura , RNA Polimerases Dirigidas por DNA , Pirróis , Transcrição Gênica , Proteínas ViraisRESUMO
tRNA:m(5)C methyltransferase Trm4 generates the modified nucleotide 5-methylcytidine in archaeal and eukaryotic tRNA molecules, using S-adenosyl-l-methionine (AdoMet) as methyl donor. Most archaea and eukaryotes possess several Trm4 homologs, including those related to diseases, while the archaeon Methanocaldococcus jannaschii has only one gene encoding a Trm4 homolog, MJ0026. The recombinant MJ0026 protein catalyzed AdoMet-dependent methyltransferase activity on tRNA in vitro and was shown to be the M. jannaschii Trm4. We determined the crystal structures of the substrate-free M. jannaschii Trm4 and its complex with sinefungin at 1.27 A and 2.3 A resolutions, respectively. This AdoMet analog is bound in a negatively charged pocket near helix alpha8. This helix can adopt two different conformations, thereby controlling the entry of AdoMet into the active site. Adjacent to the sinefungin-bound pocket, highly conserved residues form a large, positively charged surface, which seems to be suitable for tRNA binding. The structure explains the roles of several conserved residues that were reportedly involved in the enzymatic activity or stability of Trm4p from the yeast Saccharomyces cerevisiae. We also discuss previous genetic and biochemical data on human NSUN2/hTrm4/Misu and archaeal PAB1947 methyltransferase, based on the structure of M. jannaschii Trm4.